MT8950 Mitel Networks Corporation, MT8950 Datasheet - Page 12

• Manufacturer Part Number: MT8950
• Description: ISO-CMOS ST-BUS FAMILY Data Codec
• Manufacturer: Mitel Networks Corporation

MT8950
the codec cannot be used in the local carrier mode.
If this facility is to be used, an appropriate clock can
be input to the device. The long SPACE detection
circuitry and the Data Activity output can be used for
monitoring the codec if necessary.
Figure 10 shows a block diagram schematic of a
circuit which could be used to submultiplex RS-232
control signals with the data. The data and control
signals are operated on by the microprocessor or the
logic circuitry and subsequently transmitted as a
three level signal. The control signals are encoded
as bipolar violations. Since the control status does
not change very frequently during a call, this
information is transmitted only when no data is
available. Circuitry near the Codec converts the
bipolar signal into a unipolar format and inputs it at
D
the Codec output at D
to the bipolar format before being transmitted.The
Data Codec is selected to operate in the RZ format.
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1 and D
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Bipolar RZ signal
RTS
CTS
DSR
DTR
RLSD
TxD
RxD
DTE
Figure 10 - Block Diagram Illustration of a Scheme to Submultiplex RS-232 Control Signals
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Line Driver
Converter
Converter
to Bipolar
Bipolar to
Receiver
Unipolar
Unipolar
X
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2. Conversely, the low speed data from
RS-232
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ISO-CMOS
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R
Converters
1 and D
Level
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D
D
D
D
X
X
R
R
MT8950
2
1
2
1
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R
DSTo
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DSTi
2 is first converted
Receiver
Driver /
TTL
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Line
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Microcomputer
Random Logic
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or
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Converter
STo1
STi1
Bipolar
NRZ /
Digital PBX
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MT8980
MPU
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STo3
Converter
STi3
The microprocessor or the random logic circuit
examines the received signal for violations.
stream of violations is detected, then the signal is
interpreted to be control information. The detected
violations are decoded and the appropriate change
in the status of the RS-232 control signals is
implemented. If no violations are detected then the
incoming signal is considered to be the data and it is
rerouted to the RxD pin of the RS-232 connector.
The microprocessor could also be used in the initial
call setup and for error checking of the received
control information. This scheme could be used to
provide transparent modem capability to any of the
ST-BUS based equipment.
Bipolar
NRZ /
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Microcomputer
Random Logic
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or
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Receiver
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Driver /
Line
DSTi
DSTo
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TTL
MT8950
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D
D
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D
D
Converters
R
R
X
X
2
1
2
1
Level
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Bipolar RZ signal
Line Driver
Converter
to Bipolar
Converter
Bipolar to
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Receiver
Unipolar
Unipolar
RS-232
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RTS
CTS
DSR
DTR
RLSD
TxD
RxD
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DTE
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If a
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